Abstract: In a construction machine comprising an engine, hydraulic device, and heat exchanger for cooling the engine and the hydraulic device, which are all disposed in an upper rotating body of the construction machine, there is formed a maintenance passage along which maintenance portions of the engine and the hydraulic device are disposed so as to cross the upper rotating body. Exhaust air from cooling fans for sending air to the heat exchanger is discharged to the exterior of the machine body through the passage. Thus, the passage is utilized as an exhaust air passage for the heat exchanger, whereby it is possible to provide a construction machine improved in cooling efficiency for the heat exchanger.

Abstract: In a construction machine comprising an engine, hydraulic device, and heat exchanger for cooling the engine and the hydraulic device, which are all disposed in an upper rotating body of the construction machine, there is formed a maintenance passage along which maintenance portions of the engine and the hydraulic device are disposed so as to cross the upper rotating body. Exhaust air from cooling fans for sending air to the heat exchanger is discharged to the exterior of the machine body through the passage. Thus, the passage is utilized as an exhaust air passage for the heat exchanger, whereby it is possible to provide a construction machine improved in cooling efficiency for the heat exchanger.

Abstract: The invention provides a pump controller for a construction machine that allows an operator to set the maximum speed of a specific actuator arbitrarily without altering the negative control and acquire a smooth operation. The pump controller comprises a plurality of control valves to supply actuators with a controlled pressure oil, a variable displacement hydraulic pump to supply the plural control valves with the pressure oil in parallel, a center bypass connected in parallel to the control valves, and a restrictor to generate a control pressure for negatively controlling the variable displacement hydraulic pump installed at a terminal end of the center bypass.

Abstract: A flow control valve is disposed in a bleed-off line which is for returning to a tank a portion of an oil flow advancing toward a hydraulic motor from a hydraulic pump. Upon operation of a control valve in an accelerating direction, the flow control valve is operated in a closing direction with a certain time lag, while upon operation of the control valve in a decelerating direction, the flow control valve is operated in an opening direction without a time lag. By so doing, an accelerating operation can be done smoothly while maintaining a required torque.

Abstract: A hydraulic pump is driven by a first prime mover. An actuator, which is controlled by a control valve, is operated by a pressure oil fed from the hydraulic pump. A second prime mover, which is an electric motor, is provided separately from the first prime mover. A pilot pump is driven by the motor. Hydraulic oil is conducted from the pilot pump to a pilot port of the control valve through a pilot oil pipe. A remote control valve is provided in the pilot oil pipe, and change-over operation of the control valve is controlled by the remote control valve. In an on-load state, a command value for controlling the motor is set at a target current value corresponding to a normal pressure, while in an off-load state the command value is set at a target current value which is lower. By so doing, there does not occur any unnecessary power loss even in an off-load state.

Abstract: A hydraulic control apparatus having two groups and formed by combination of actuator circuits on large flow rate side (a boom cylinder circuit and an arm cylinder circuit) and actuator circuits on small flow rate side (a bucket cylinder circuit and a rotating motor circuit), for independent supply of hydraulic fluid. In these groups, a bucket preferential valve and a rotating preferential valve form bucket cylinder preferential and rotating motor preferential circuit constitutions.